Fan blade retaining structure

ABSTRACT

A disk  10  includes a plurality of dovetail grooves  12  which are spaced at a predetermined angular interval in a circumferential direction and extend in an axial direction. A fan blade  20  includes a dovetail part  22  which is fitted to each of the dovetail grooves in an axial direction and capable of transmitting a centrifugal force produced during rotation to the disk. The disk further includes a flange part  14  which is positioned in front of the dovetail grooves and extends outward in a radial direction. A ring-shape retainer member  30  is fitted between a front surface  22   a  of the dovetail part  22  and a rear surface  16   a  of the flange part  14  and transmits an axial forward load acting on the fan blade  20  to the disk  10  via the rear surface  16   a  of the flange part.

TECHNICAL FIELD

The present invention relates to a fan blade retaining structure forpreventing a fan blade from coming off from a disk even when an axialforward load acts on the fan blade upon breaking the fan blade.

BACKGROUND ART

FIG. 1 is a schematic view illustrating a turbofan engine 110 for anairplane. The engine 110 includes a fan assembly 112 which is coaxiallydisposed with respect to a center shaft 116 and is driven by a coreengine 114. During the operation of the engine 110, external air 118 issucked by the fan assembly 112 so as to produce a thrust for enabling anairplane to fly.

When the airplane having the above-described engine 110 takes off orlands, for example, a comparatively large bird 120 may be sucked intothe fan assembly 112. In this case, the bird 120 impacts on fan blades122 extending outward from a rotor disk 124 in a radial direction, sothat a part of the fan blades 122 is broken and scattered. Additionally,alien materials except for the bird may be sucked into the fan assemblyto thereby damage components. In addition to the supposition, the fanblades 122 or a part thereof may be broken and scattered due to a largeload or the like. Hereinafter, such a phenomenon will be referred to asFBO (Fan Blade Off).

In the event of the FBO, a part of the fan blades 122 may be scatteredto collide against the adjacent other fan blades 122, so that an axialforward (upstream) shock power acts on the fan blades 122.

Since the axial forward shock power acting on the fan blades 122 acts ina direction in which the fan blades 122 come off from the rotor disk124, the fan assembly 112 needs to be provided with a structure capableof retaining the fan blades 122 in the rotor disk 124 even when theaxial forward shock power acts on the fan blades 122.

Patent Document 1 has already proposed a fan blade retainer forsatisfying the above-described requirements.

Patent Document 1 discloses a retainer assembly 126 for retaining thefan blades 122 in the rotor disk 124. As shown in FIG. 2, the retainerassembly 126 includes the rotor disk 124, a first blade retainer 138,and a second blade retainer 144.

The rotor disk 124 includes a plurality of dovetail posts 128 which arespaced at a predetermined angular interval in a circumferentialdirection, and a dovetail groove 130 is formed therebetween. Each fanblade 122 includes a dovetail 132 fitted to the dovetail groove 130 inan axial direction, and the dovetail 132 is immovably retained in aradial direction by the dovetail post 128. With the above-describedconfiguration, a centrifugal force produced during rotation of the fanblades 122 is transmitted to the rotor disk 124 via the dovetail post128.

The first blade retainer 138 is provided so as to prevent the fan blade122 from moving in an axial forward direction (upstream direction). Thefirst blade retainer 138 includes a fixed plate 140 fixed to the rotordisk 124 so as to immovably retain the fan blade 122 in the dovetailgroove 130 in an axial direction. The fixed plate 140 is inserted in anoutward radial direction into a pair of grooves 142 formed in theadjacent dovetail posts 128.

The second blade retainer 144 is provided so as to prevent the axialmovement of the fan blades 122 by serving as a chock after the fanblades 122 move by a predetermined distance in a case where the axialmovement of the fan blades 122 cannot be prevented by the first bladeretainer 138. With the above-described configuration, both the firstblade retainer 138 and the second blade retainer 144 disperse the axialforward shock energy acting on the fan blades 122 so that each fan blade122 is retained in the dovetail grooves 130.

[Patent Document 1]

U.S. Pat. No. 5,282,720 ‘Fan blade retainer’

FIG. 3 is a schematic view illustrating a dovetail structure accordingto a conventional art. As shown in the drawing, it is necessary toattach the fan blades of the turbofan engine to a peripheral portion ofa circular disk (called a fan disk or a spinner) rotationally driven bya turbine. For this reason, in the past, there was adopted aconventional dovetail structure in which a dovetail part is formed in aroot portion of the fan blade so as to extend in a longitudinaldirection and the dovetail part is fitted to a dovetail groove formed inthe periphery of a disk.

In addition, in order to prevent the fan blade from coming off from thedovetail groove due to the axial forward power, in the past, a membercalled a retainer was fastened to a front portion of the blade byfastening bolts, nuts, and the like.

Examples of the retainer include a circular-ring type for functioningwith respect to a plurality of blades and a plate type for functioningwith respect to each of the blades.

However, in case of the circular-ring type retainer, since a gap betweenan action portion of a load and a fastening portion such as a bolt and anut is long, a problem arises in that the stress acting on the bolt dueto the load is difficult to be estimated and the retainer is difficultto be designed. Meanwhile, in case of the plate type retainer, since theretainer is mounted to each blade, a problem arises in that operabilityis poor. For this reason, in both cases of the circular-ring typeretainer and the plate type retainer, a problem arises in that adecrease in weight is difficult to be achieved and a cost is high.

In addition, in case of the retainer assembly described in PatentDocument 1, although both the first blade retainer 138 and the secondblade retainer 144 can disperse the axial forward shock energy acting onthe fan blades 122 so that each fan blade 122 is retained in thedovetail groove 130, a problem arises in that the structure is complexand a manufacturing cost is high.

In the retainer assembly, since it is necessary to provide a pluralityof first blade retainers 138 and the second blade retainers 144, aproblem arises in that the operability during an assembling operation ispoor.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

The present invention is contrived in consideration of theabove-described problems. That is, an object of the invention is toprovide a fan blade retaining structure capable of surely preventing afan blade from coming off from a disk even when an axial forward loadacts on the fan blade upon breaking the fan blade, of being easilydesigned with high estimation precision of stress, and of enabling afastening bolt to be lighter in weight, smaller in size, and fewer innumber than a conventional fastening bolt, thereby reducing the numberof components. Accordingly, it is possible to provide the fan bladeretaining structure capable of realizing a decrease in weight and cost.

According to the invention, there is provided a fan blade retainingstructure in which a plurality of fan blades is configured to beattached to an outer periphery of a disk rotationally driven by aturbine, wherein the disk includes a plurality of dovetail groovesconfigured to be spaced at a predetermined angular interval in acircumferential direction and to extend in an axial direction, whereineach of the fan blades includes a dovetail part configured to be fittedto each of the dovetail grooves in an axial direction and capable oftransmitting a centrifugal force produced during rotation to the disk,wherein the disk further includes a flange part configured to bepositioned in front of the dovetail grooves and to extend outward in aradial direction, and wherein the fan blade retaining structure furtherincludes a ring-shape retainer member configured to be fitted between afront surface of the dovetail part and a rear surface of the flange partso as to transmit an axial forward load acting on the fan blade to thedisk via the rear surface of the flange part.

According to a preferred embodiment of the invention, the flange part ofthe disk includes disk tooth parts configured to be spaced at apredetermined angular interval in a circumferential direction and toproject outward in a radial direction.

The retainer member includes a ring part configured to have a rearsurface coming into contact with the front surface of the dovetail partand retainer tooth parts configured to be formed inside the ring part soas to be spaced at a predetermined angular interval in a circumferentialdirection and to project inward in a radial direction.

Each of the retainer tooth parts is capable of passing between theadjacent disk tooth parts in an axial direction and comes close to therear surface of the disk tooth part to overlap therewith at the sameposition in a circumferential direction.

The fan blade retaining structure further includes a fastener configuredto fix the retainer tooth part to the disk tooth part in a state wherethe retainer tooth part comes close to the disk tooth part to overlapwith each other.

The disk tooth part is desirably formed at a position between theadjacent dovetail grooves in a circumferential direction.

The disk tooth part is desirably formed at the same position as that ofthe dovetail groove in a circumferential direction.

According to the configuration of the invention, since the retainermember is provided so as to be fitted between the front surface of thedovetail part and the rear surface of the flange part, even when theaxial forward load acts on the fan blades upon breaking the fan blades,it is possible to transmit the axial forward load from the front surfaceof the dovetail part to the disk via the rear surface of the flange partand the retainer member.

Since a stress occurring in the retainer member by the axial forwardload mainly corresponds to an axial compressive stress and a stressoccurring in the flange part by the axial forward load mainlycorresponds to an axial stretching stress, it is possible to accuratelyestimate an internal stress occurring in the retainer member and theflange part in accordance with the axial forward load.

Since the retainer member and the flange part are prevented from beingbroken by setting the internal stress to a sufficiently small stress, itis possible to surely prevent the fan blade from coming off from thedisk.

Since the ring-shape retainer member is used, it is possible to reducethe number of components.

Since the axial forward load does not act on the fastener (bolt, nut,and the like) for fastening the retainer member to the flange part bytransmitting the axial forward load to the retainer member and theflange part, it is possible to more reduce the weight, the size, and thenumber of the fastening bolt than a conventional fastening bolt, andthus to reduce the number of components. Accordingly, it is possible torealize a decrease in weight and cost.

In addition, the flange part includes the disk tooth parts which projectoutward in a radial direction and the retainer member includes the ringpart which comes into contact with the front surfaces of the dovetailparts and the retainer tooth parts which project inward in a radialdirection. Also, each of the retainer tooth parts can pass between theadjacent disk tooth parts in an axial direction and is disposed adjacentto each rear surface of the disk tooth parts.

Accordingly, the retainer member can be easily fitted between the fontsurface of the dovetail parts and the rear surface of the flange part insuch a manner that the retainer tooth parts of the retainer member passbetween the adjacent disk tooth parts in an axial direction and arerotated up to the same positions in a circumferential direction so as tobe adjacent to the rear surfaces of the disk tooth part.

Since the axial forward load does not act on the fastener by fixing theretainer tooth parts to the disk tooth parts at the same positions in acircumferential direction by using the fastener (bolt, nut, and thelike), it is possible to more reduce the weight, the size, and thenumber of the fastener than the conventional fastener, and thus toreduce the number of components.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view illustrating a turbofan engine for anairplane.

FIG. 2 is a configuration view illustrating a fan blade retainerdisclosed in Patent Document 1.

FIG. 3 is a schematic view illustrating a dovetail structure accordingto a conventional art.

FIG. 4 is an overall perspective view illustrating a state where a fanblade retaining structure according to the invention is disassembled.

FIG. 5A is a transverse sectional view illustrating an engine providedwith the fan blade retaining structure according to the invention.

FIG. 5B is an enlarged view illustrating a B part shown in FIG. 5A.

FIG. 6A is a view taken along the line C-C shown in FIG. 5B in a statewhere a retainer member is being mounted.

FIG. 6B is a view taken along the line C-C shown in FIG. 5B in a statewhere the retainer member is completely mounted.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, preferred embodiments of the invention will be described indetail with reference to the accompanying drawings. In addition, in therespective drawings, the same reference numerals are given to the samecomponents and the repetitive description thereof will be omitted.

FIG. 4 is an overall perspective view illustrating a state where a fanblade retaining structure according to the invention is disassembled.The fan blade retaining structure according to the invention isconfigured such that a plurality of fan blades 20 are attached to theouter periphery of a disk 10 which is rotationally driven by a turbine(not shown).

As shown in the drawing, the fan blade retaining structure according tothe invention includes the disk 10, the fan blades 20, a retainer member30, and a fastener 40.

The disk 10 includes a plurality of dovetail grooves 12 which are spacedat a predetermined angular interval in a circumferential direction andextends in an axial direction. Although it is desirable that the numberof the dovetail grooves 12 is the same as that of the fan blades 20, aplurality (two or more) of fan blades 20 may be attached to one dovetailgroove 12.

In this example, the dovetail grooves 12 are parallel to a shaft center1 of a rotary shaft, but may be inclined with respect to the shaftcenter 1. In addition, each of the dovetail grooves 12 may be formedinto a linear shape or a circular arc shape so long as each of the fanblades 20 is inserted and fitted in an axial direction from the frontside.

The fan blade 20 includes a dovetail part 22 which is formed in theinner end in a radial direction so as to be fitted to the dovetailgroove 12. The dovetail part 22 is configured to be fitted to thedovetail groove 12 in an axial direction from the front side and totransmit a centrifugal force acting on the fan blade 20 produced duringrotation to the disk 10.

FIG. 5A is a transverse sectional view illustrating a fan part of anengine provided with the fan blade retaining structure according to theinvention, in which only the upper side of the shaft center 1 of therotary shaft is shown. FIG. 5B is an enlarged view illustrating a B partshown in FIG. 5A.

In addition, in the drawing, Reference numeral 1 denotes the shaftcenter of the rotary shaft of the disk 10 and the fan blade 20,Reference numeral 2 denotes an air flow passage, Reference numeral 3denotes the inner peripheral surface of the air flow passage, Referencenumeral 4 denotes an intake air flow, and Reference numeral 5 denotes anaxial forward power acting on the fan blade 20 in the event of FBO.

As shown in FIGS. 4, 5A, and 5B, the disk 10 further includes a flangepart 14 which is positioned in front of the dovetail groove 12 andextends in a radial outer direction. The flange part 14 is integrallyconnected to a hollow cylindrical part 13 which extends forward from theinner end of the disk 10.

The flange part 14 further includes disk tooth parts 16 which are spacedat a predetermined angular interval in a circumferential direction andproject outward in a radial direction.

The retainer member 30 includes a hollow disk-shape ring part 32 andretainer tooth parts 34 which are integrally formed with the innerportion of the ring part 32.

The ring part 32 includes a rear surface 32 a, and the rear surface 32 acomes into contact with a front surface 22 a of the dovetail part 22inserted into the dovetail groove 12.

In addition, the retainer tooth parts 34 are spaced at a predeterminedangular interval in a circumferential direction and project inward in aradial direction.

As shown in FIG. 4, in this example, the disk tooth parts 16 are formedat centers in a circumferential direction of the dovetail grooves 12which are adjacent to each other in a circumferential direction and arenot positioned on extension lines of the dovetail grooves 12.Accordingly, in this example, the retainer tooth parts 34 are formed ina circumferential direction so as to have the same pitches as those ofthe dovetail grooves 12 and have the same number as that of the dovetailgrooves 12.

With the above-described configuration, the disk tooth parts 16 can beformed at the radial positions so as to have the substantially sameheights as those of the dovetail parts 22, and the forward axial loadproduced from the dovetail parts 22 can be surely supported by two disktooth parts 16 in a circumferential direction.

In addition, the invention is not limited to this configuration, but thedisk tooth parts may be formed at the same positions as those of thedovetail grooves in a circumferential direction.

In this case, although the disk tooth parts 16 need to be formed at theradial positions lower than the bottom portions of the dovetail parts 22so as not to be positioned on the extension lines of the dovetailgrooves 12, the axial forward load produced from the dovetail parts 22can be surely supported by the disk tooth parts 16 disposed at the samepositions in a circumferential direction.

In addition, the number of the disk tooth parts 16 and the retainertooth parts 34 needs not to be the same as that of the dovetail grooves12, but the number may be two or more (for example, four, eight, sixteenor the like) so long as a balance is ensured during a high-speedrotation.

FIG. 6A is a view taken along the line C-C shown in FIG. 5B in a statewhere the retainer member is being mounted. FIG. 6B is a view takenalong the line C-C shown in FIG. 5B in a state where the retainer memberis completely mounted.

In FIGS. 4 to 6A and 6B, an axial distance (thickness) from the rearsurface 32 a of the retainer member 30 to each front surface 34 a of theretainer tooth parts 34 is set to be a smaller value than an axialdistance from the front surface 22 a of the dovetail part 22 to eachrear surface 16 a of the disk tooth parts 16 in a mounting state. It isdesirable that the gap is set so that the retainer member 30 smoothlyrotates about the shaft center 1 in a state where the retainer member ismounted.

As shown in FIG. 6A, each of the retainer tooth parts 34 can passbetween the adjacent disk tooth parts 16 in an axial direction. Inaddition, as shown in FIG. 6B, the retainer tooth parts come close tothe rear surfaces of the disk tooth parts 16 to overlap therewith at thesame positions in a circumferential direction by rotating the retainermember 30 about the shaft center 1 by a predetermined angle (in thisexample, 30 degree or so). It is desirable that the close gaptherebetween is set to be small so long as the retainer tooth parts donot interfere with the disk tooth parts within an operation temperaturerange of the engine.

In FIGS. 4, 5A, and 5B, the fastener 40 includes a bolt 41 and a nut 42which are screw-connected to each other while passing through a throughhole 35 formed in the retainer member 30 and a through hole 17 formed inthe flange part 14 of the disk 10 so as to fix the retainer tooth parts34 and the disk tooth parts 16 at the same positions in acircumferential direction.

In addition, in this example, the flange part 14 extends inward in aradial direction, and the through hole 17 is formed in the extendingportion. An inverse L-shape portion is formed in the retainer member 30so as to come into contact with the extending portion, and the throughhole 35 is formed in the inverse L-shape portion.

However, the invention is not limited to this configuration, but may beconfigured such that the retainer member 30 is formed into, for example,a ring-shape flat plate instead of the inverse L-shape portion and thering-shape flat plate is directly fixed to the disk 10.

With the above-described configuration, the retainer tooth parts 34 andthe disk tooth parts 16 are fixed at the same positions in acircumferential direction during the time when the ring-shape retainermember 30 shown in FIG. 6B is completely mounted and the engine isoperated.

In addition, the retainer member 30 can transmit the axial forward loadacting on the fan blade 20 to the disk 10 via the rear surfaces 16 a ofthe disk tooth parts 16 while being fitted between the front surfaces 22a of the dovetail parts 22 and the rear surfaces 16 a of the disk toothparts 16.

With the above-described configuration, since there is provided theretainer member 30 fitted between the front surfaces 22 a of thedovetail parts 22 and the rear surfaces 16 a of the flange part 14 (thedisk tooth parts 16), even when the axial forward load occurs acts onthe fan blade upon breaking the fan blade 20, the axial forward load canbe transmitted from the front surfaces 22 a of the dovetail parts 22 tothe disk 10 via the retainer member 30 and the rear surfaces 16 a of theflange part.

Since a stress occurring in the retainer member 30 by the axial forwardload mainly corresponds to an axial compressive stress and a stressoccurring in the flange part 14 by the axial forward load mainlycorresponds to an axial stretching stress, it is possible to accuratelyestimate an internal stress occurring in the retainer member 30 and theflange part 14 in accordance with the axial forward load.

Since the retainer member 30 and the flange part 14 are prevented frombeing broken by setting the internal stress to a sufficiently smallstress, it is possible to surely prevent the fan blade 20 from comingoff from the disk 10.

Since the ring-shape retainer member 30 is used, it is possible toreduce the number of components.

Since the axial forward load does not act on the fastener 40 (bolt, nut,and the like) for fastening the retainer member 30 to the flange part 14by transmitting the axial forward load to the retainer member 30 and theflange part 14, it is possible to more reduce the weight, the size, andthe number of the fastener 40 than a conventional fastener, and thus toreduce the number of components.

In addition, the flange part 14 of the disk 10 includes the disk toothparts 16 which project outward in a radial direction and the retainermember 30 includes the ring part 32 which comes into contact with thefront surfaces 22 a of the dovetail parts 22 and the retainer toothparts 34 which project inward in a radial direction. Also, each of theretainer tooth parts 34 can pass between the adjacent disk tooth parts16 in an axial direction and is disposed adjacent to each rear surface16 a of the disk tooth parts 16. Accordingly, the retainer member 30 canbe easily fitted between the font surface 22 a and the rear surface 16 aof the flange part in such a manner that the retainer tooth parts 34 ofthe retainer member 30 pass between the adjacent disk tooth parts 16 inan axial direction and are rotated up to the same positions in acircumferential direction so as to be adjacent to the rear surfaces ofthe disk tooth part 16.

Since the axial forward load does not act on the fastener 40 by fixingthe retainer tooth parts 34 to the disk tooth parts 16 at the samepositions in a circumferential direction by using the fastener 40 (bolt,nut, and the like), it is possible to more reduce the weight, the size,and the number of the fastener than the conventional fastener, and thusto reduce the number of components.

The invention is not limited to the preferred embodiments, but may be,of course, modified variously in the scope without departing from thespirit of the invention.

1. A fan blade retaining structure in which a plurality of fan blades isconfigured to be attached to an outer periphery of a disk rotationallydriven by a turbine, wherein the disk includes a plurality of dovetailgrooves configured to be spaced at a predetermined angular interval in acircumferential direction and to extend in an axial direction, whereineach of the fan blades includes a dovetail part configured to be fittedto each of the dovetail grooves in an axial direction and capable oftransmitting a centrifugal force produced during rotation to the disk,wherein the disk includes a flange part configured to be positioned infront of the dovetail grooves and to extend outward in a radialdirection, and wherein the fan blade retaining structure furthercomprises a ring-shape retainer member configured to be fitted between afront surface of the dovetail part and a rear surface of the flange partso as to transmit an axial forward load acting on the fan blade to thedisk via the rear surface of the flange part.
 2. The fan blade retainingstructure according to claim 1, wherein the flange part of the diskincludes disk tooth parts configured to be spaced at a predeterminedangular interval in a circumferential direction and to project outwardin a radial direction, wherein the retainer member includes a ring partconfigured to have a rear surface coming into contact with the frontsurface of the dovetail part and retainer tooth parts configured to beformed inside the ring part so as to be spaced at a predeterminedangular interval in a circumferential direction and to project inward ina radial direction, and wherein each of the retainer tooth parts iscapable of passing between the adjacent disk tooth parts in an axialdirection and comes close to the rear surface of the disk tooth part tooverlap therewith at the same position in a circumferential direction.3. The fan blade retaining structure according to claim 2, furthercomprising: a fastener configured to fix the retainer tooth part to thedisk tooth part in a state where the retainer tooth part comes close tothe disk tooth part to overlap with each other.
 4. The fan bladeretaining structure according to claim 2, wherein the disk tooth part isformed at a position between the adjacent dovetail grooves in acircumferential direction.
 5. The fan blade retaining structureaccording to claim 2, wherein the disk tooth part is formed at the sameposition as that of the dovetail groove in a circumferential direction.